test_runner: detect only tests when --test is not used

This commit updates the way the test runner processes 'only' tests when node:test files are run without the - test CLI.

The first two commits here are from https://github.com/nodejs/node/pull/54832. Please ignore them while reviewing. The third commit is a breaking change.

I was going to wait to open this PR until #54832 landed, but it's taking longer than expected because of CI flakiness, so I figured I would get the 48 hour clock started on this change.